Recently, with the generalization of information communication services, the advent of various multimedia services, and the advent of high quality services, there is an increasing demand for wireless communication services. To actively cope with such a demand, capacity of a communication system should be increased. To increase communication capacity in a wireless communication environment, a method for newly detecting an available frequency band and a method for increasing efficiency of given resources may be considered. Of the methods, an example of the latter method includes a multiple antenna transceiver technique, which has recently received much attention and is actively being developed. The multiple antenna transceiver technique includes obtaining diversity gain by providing a plurality of antennas in a transceiver and additionally ensuring a spatial region for utilizing resources, or increasing transmission capacity by transmitting data in parallel through two or more transmit antennas.
An example of the multiple antenna transceiver technique includes multiple-input multiple-output (MIMO). The MIMO designates an antenna system having multiple inputs and outputs, and can enhance the amount of information by transmitting different kinds of information to each transmitting antenna and enhance reliability of transmission information by using a spatial domain coding scheme such as space-time coding (STC).
Supposing that the number of antennas in a transmitter of the MIMO system and the number of antennas in a receiver of the MIMO system are M and N, respectively, the M transmitting antennas may transmit independent symbols and/or spatially coded symbols by using the same frequency at the same time. Although the respective symbols transmitted from the several transmit antennas simultaneously undergo different fading which is spatially independent while passing through a wireless channel due to spatial scattering effect, such a randomness characteristics of the spatial channel may allow decoupling simultaneously transmitted data symbols at the receiver. The aforementioned MIMO system can be combined with an orthogonal frequency division multiplexing (OFDM) system to enable efficient data transmission.
In addition to the MIMO system, link control schemes such as adaptive modulation and coding (AMC), hybrid automatic request (HARQ), and power control can be used for efficient data transmission. The AMC means a channel adaptive transmission scheme which allows a base station to determine a modulation mode and a coding rate based on feedback information received from terminals and to control a data rate in accordance with the determined modulation mode and coding rate. According to an example of the AMC, if the base station determines a modulation and coding set (MCS) based on CQI information fed back from a terminal and transmits the determined MCS, the terminal transmits data by using a modulation scheme and a coding scheme, which are designated in the MCS.
In general, schemes which enhance system performance through feedback, such as AMC, exert their maximum performance if feedback information such as channel status and motion speed of a user is transmitted from a receiving side whenever data transmission is performed. However, if feedback information is transmitted whenever data transmission is performance, a problem occurs in that overhead excessively occurs in a feedback channel.
Particularly, in a multiple antenna system which uses multiple codeword (MCW), since different MCSs can be set for each codeword, CQI equivalent to the number of codewords should be fed back to enhance system performance. However, this causes overhead to the feedback channel as described above.